al vs scandium? for bikes, in SAME tube thickness/profile think longer life for an sc frame, but then it’s usually used in a thinner tube ‘cos it’s stronger and the whole point of using it in bikes is to get a lighter frame with similar strength characteristics.

whatever people tell you, most race teams will use at least a couple of al / sc race frames per rider per season. personally, i wouldn’t choose to ride either an al or sc frame more than two years old. but ymmv.

You’ll never get near the fatigue life for aluminium on a bike. If an aluminium frame fails it’ll be on a weld/junction not the frame itself. Aircraft grade aluminium (which is used on most bikes (2024 or 6061)) is suitable for aircraft wings (turbulence), multiple pressurisations (fuselage) and impacts (ground handling) over the 50-80 year lifespan, they don’t crash due to material failure.

Scandium is NOT usually used to make a lighter bike scandium is an aluminium alloy frame with scandium alloy tubes. Scandium is used as it’s stronger than aluminium but more brittle, it can therefore be used to create thinner tube profiles and which give a different feel of ride.

omg, is there ANYTHING more boring than a discussion on frame materials…?

but on the basis that you, dear duffy, are talking out of the orifice in your bottom, let’s review.

aircraft life is not measured in years, but in stress cycles. it’s called ‘airframe life’ and is a highly complex subject. but it’s important primarily because al DOES fatigue, and not always in a highly predictable manner. crack testing is an integral part of aircraft maintenance.

sadly, aircraft do crash – regularly – due to materials failure. i would take the time to educate you on this, but google will do a far better job than i. search for articles on the fatigue failure of the ‘Comet’ airliner and take it from there…

fatigue as it applies to composites is a far more interesting topic. should we discuss this?

i fully agree with you on the weld/tube junction being a major failure point on modern bicycle frames, but that’s also a function of the material and the way it reacts to localized heat stress, no?. you may also have mentioned WHY certain al frames are heat-treated after welding…

scandium IS (generally) used to create a lighter frame, or a stronger frame for the same tube thickness/profile. go speak to a frame designer.

if there is anything else i can help you with, dear child, you have only to ask.

I didn’t really want to get in to this but, Aircraft don’t crash regularly due to materials failure, they crash due to: component; maintenance; environmental and human factors far more often than material failure.

The Comet is the worst example you could chose, NOTHING was known about the effect of repeated presurisation (metal fatigue) effects of aircraft until the Comet. The only reason that the material failed was due to the improper use of square windows, creating a stress concentration point in the frame design.

Speaking of frame design – I did speak to a frame designer, Brant…you know Brant right?

Also. If scandium is used to create a lighter frame, how come the Kona Kula Primo (scandium) is the same weight as the Kona Kula (Aluminium)

Fatigue of composites is a far more complex topic but I’d hardly call it intersting. I do have some experience of materials technology and am currently working on a project for EADS Astrium.

If you can help me with the finite element/topology optimisation of the primary composite structure of a Mercury space probe, by all means e-mail me, I could use the help.

The Comet is the worst example you could chose, NOTHING was known about the effect of repeated presurisation (metal fatigue) effects of aircraft until the Comet. The only reason that the material failed was due to the improper use of square windows, creating a stress concentration point in the frame design.

So. The Comet was an example of metal fatigue or not? Yes, metal fatigue caused by a design error, but metal fatigue nevertheless.

Speaking of frame design – I did speak to a frame designer, Brant…you know Brant right?

No. I have no idea who Brant is. But I know half the design team on the Eurofighter. Does that mean I win the ‘who has the biggest balls’ contest?
Also. If scandium is used to create a lighter frame, how come the Kona Kula Primo (scandium) is the same weight as the Kona Kula (Aluminium)

Again, I have no idea of the comparative tube profiles or design criteria to which the Kona design team were working on these two bikes. Do you? I thought not.

We were talking generally about the relative merits of frame materials. I believe my points retain their validity, though you clearly question that assumption. Fine by me.

Fatigue of composites is a far more complex topic but I’d hardly call it intersting.

Again, to each his own…

If you can help me with the finite element/topology optimisation of the primary composite structure of a Mercury space probe, by all means e-mail me, I could use the help.

I’m sure you could, especially based on what you’ve written thus far. An open mind, and an ability to see the bigger picture, is a useful attribute for a design engineer.

And if you haven’t been granted access to / developed for yourself, some nice little computer models to help you with your analysis, I fear for the future of the cute little probe. Please, tell me you’ll have someone check your work?

Oh, I’ve an eighteen month old ‘dale you might like to purchase. It’s been thrashed to hell and back but I’m sure it will ‘last a lifetime’ ‘cos al ‘does not fail’. You can put your ass on it down the next super-steep mountain path you come across…

Oh, I’ve an eighteen month old ‘dale you might like to purchase. It’s been thrashed to hell and back but I’m sure it will ‘last a lifetime’ ‘cos al ‘does not fail’.

Where does the nicknane CrackandFail come from then?
I’ve broken at least 3 aluminium frames and 3 or 4 aluminium swingarms (and one steel frame) all breaks where adjacent to welds (none of them were Cannondale BTW).

the whole point of using it in bikes is to get a lighter frame with similar strength characteristics.

So. Kona made their top end frame out of scandium for shits and giggles? As it ain’t any lighter.

Speaking of frame design – I did speak to a frame designer, Brant…you know Brant right?

No. I have no idea who Brant is. But I know half the design team on the Eurofighter. Does that mean I win the ‘who has the biggest balls’ contest?

That really depends doesn’t it? in Aviation engineering, yes I suppose so but, we’re talking about a (I’m assuming given the forum we’re on) bike frame. I was using aircraft as an extreme example of aluminium fatigue, stating that a bike would get nowhere near the same levels of induced stress…surely you agree on this? Brant is Brant Richards AKA the owner or On-One bikes…A frame designer which is what you asked for. No?

‘last a lifetime’ ‘cos al ‘does not fail’

I never said either of these things. However, how much mountain biking kit is made of Aluminium? If it were half as bad as you imply how could anyone offer the 5-10 year warranties?

And if you haven’t been granted access to / developed for yourself, some nice little computer models to help you with your analysis, I fear for the future of the cute little probe. Please, tell me you’ll have someone check your work?

I have a graph somewhere showing the fatigue life of aluminium against the amplitude of the cycles it’s experiencing. Bottom line obviously is that the more you bend it, the sooner it’s likely to break, but the graph isn’t linear. Will try to dig it out for you.

sadly, aircraft do crash – regularly – due to materials failure. i would take the time to educate you on this, but google will do a far better job than i. search for articles on the fatigue failure of the ‘Comet’ airliner and take it from there…

ro wins the strawman of the year competition with that little gem of his. So to support your assertion that “aircraft do crash regularly due to materials failure” (I note you don’t actually use the word “fatigue”) you’re introducing as evidence crashes which happened 50 years ago to aircraft designed by people who didn’t actually understand metal fatigue? Strangely you seem to have used the present tense in your assertion though.

‘TandemJeremy’ why are you being such a buffoon? all you have to do is spend three seconds on google. like i said, go google ‘metal fatigue airliner aircraft’. granted, it’s not always al which fails, but it usually is 🙂

strangely, there is more to my life than arguing nonsense with ninnies. believe what you will, a well constructed steel or ti frame is currently the best all-round mtb frame material – until the composite guys get their act together, which at the present rate of progress will be in around 20 years time.

I once watched a grown man cry because his hand made in the USA Ti frame had just snapped at the chain stay bottom bracket weld. We cruelly laughed because he had bored the @rse off us going on about how tough Ti frames were and how it was the last frame he would ever buy 😆

Wow. A 12 year old report of an already old bike. Surely there must have been something from this century? After all that’s a bit like basing your entire civil engineering industry on what happened to the Tay Bridge.

Hey, I did part of my medical training in sunny Dundee so stop dissing the Tay Bridge. It’s super-cool, even the remnants sticking out the water from the old one!

That ‘last century’ report took some finding. Do people generally write up pieces on frame failures? They’re a fact of life, aren’t they?

The OP asked whether al had a fatigue life. It does. Probably the worst of the common materials (and here I exclude Italian carbon-fibre) used to build bike frames. And using al in a mtb frame generally gives a light but fatigue-life-limited bike.

“a well constructed steel or ti frame is currently the best all-round mtb frame material”

Except that you could make an alu frame at the same weight as a typical steel one and it wouldn’t fail due to fatigue in a lifetime of use. So explain to me why the steel one is better?

“The OP asked whether al had a fatigue life.”

He did – though he didn’t mention frames – you brought that up. In fact his later post which you ignored mentioned a seatpost – so should we be using steel or ti for seatposts (and handlebars)? If alu is OK there, why not for frames?

Except that you could make an alu frame at the same weight as a typical steel one and it wouldn’t fail due to fatigue in a lifetime of use. So explain to me why the steel one is better?

Well, I could sit and explain to you the difference in fatigue properties between steel and aluminum, but I suspect you probably know them already and are just winding me up, which is Just Not Right. Stop it, please 🙂

He did – though he didn’t mention frames – you brought that up. In fact his later post which you ignored mentioned a seatpost – so should we be using steel or ti for seatposts (and handlebars)? If alu is OK there, why not for frames?

Hey, place your genitals/rest you hands on top of whatever material you like, I’ve had enough al component failures – including a one-day-old 3T stem on my road bike – to last me a lifetime. Ti / steel (where its available) may be pricey, but I’d kinda like my beautiful body to remain relatively scar-free.

Now off you got to bed, you naughty little chap.. And give my regards to your mother.

Just thought I’d take this opportunity to point out that the Comet is still flying in the guise of the Nimrod and it has never fallen out of the sky because of metal fatigue. The fatigue life on it is better than most aircraft which is why they are (maybe sometime) upgrading it to the MRA4. I really doubt that many bike frames fail because of it either. Crap welding, design or impacts are more likely. The 2 year figure seemingly plucked from nowhere earlier in the thread seems a bit drastic and I for one can’t afford to shell out for a new bike every 2 years. I wonder if my insurance will pay out if my frame fails and puts me in hospital when they find out that frames only have a safe life of 2 years?

right here we go
do aluminium alloys have a fatigue life – yes, all metals do
issue is what do you need to get fatigue failure?

well you need repeated cycling (!) of a component with stresses within the component getting near to the yield strength of the metal

so bad design is the main issue and typically the designers of aluminium alloy bikes are trying to take advantage of the lower density of aluminium to make lighter bikes – i’m pretty sure that when alu’ alloys first started being made failures where much more common than they are now

secondary issue is faults within components – poor weld practise, notches that act as stress raisers, inherent material defects acting as stress raisers meaning that though the design was strong enough the component will fail as a result of cyclical loading – and certainly i’ve seen photos on here of failed components where the fracture has some element of fatigue failure

how long will a bike last? – no idea.
how long will a bike last from a reputable mnf with a lot of experience in bikes of that type of design with good quality control? – probably longer than i will

if i was a lardy guy pushing the limits on my bike day in day out with the seat post pretty extended might have some concerns especially if has any dints or deep gouges or you can see any corrosion down the inside – how long – F knows just buy from a reputable mnfr – lightweight non abusers will rule the world

But I think the lesson is that if that the designer/engineer takes into account the characteristics of the material, then it should last as long as the design parameters say. In other words beware of amateur frame designers with new materials.